(1) Field of the Invention
The present invention generally relates to a valve operating apparatus of an internal combustion engine, and more particularly to a valve operating apparatus which operates an intake valve or an exhaust valve of an internal combustion engine by using an electromagnetic force.
(2) Description of the Related Art
A conventional valve operating apparatus which operates a valve element (either an intake valve or an exhaust valve of an engine) by using an electromagnetic force is known. For example, Japanese Laid-Open Patent Application No.61-237810 teaches such an apparatus.
The conventional device in the above-mentioned publication includes valve springs which set a plunger at a neutral position by biasing forces of the valve springs. A valve element is fixed to the plunger. When the plunger is at the neutral position, the biasing forces of the valve springs are in an equilibrium condition and the valve element is held at this position. A first solenoid coil generates an electromagnetic force to move the plunger in a valve-closing direction when current is supplied to the first solenoid coil. A second solenoid coil generates an electromagnetic force to move the plunger in a valve-opening direction when current is supplied to the second solenoid coil. A third solenoid coil generates an electromagnetic force to adjust a position of a stem of the valve element in an axial direction of the stem when current is supplied to the third solenoid coil.
The above-mentioned device can move the valve element in the valve-opening direction or in the valve-closing direction from the neutral position by supplying current to the first or second solenoid coil. Also, the above-mentioned device can adjust the neutral position of the plunger by controlling the current supplied to the third solenoid coil.
If the neutral position of the plunger is modified to a new position near the valve-closing end, it is possible to hold the valve element in a valve-closed condition by supplying a small quantity of current to the first solenoid coil. If the neutral position of the plunger is modified to another new position near the valve-opening end, it is possible to hold the valve element in a valve-opened condition by supplying a small quantity of current to the second solenoid coil.
The above-mentioned device can perform the valve opening and closing operations with a reduction of electric power consumption by modifying the neutral position of the plunger. For example, when a required period for the valve-closed condition of the valve element is relatively long, the neutral position of the plunger is adjusted nearer to the valve-closed end to reduce the electric power consumption. When a required period for the valve-opened condition of the valve element is relatively long, the neutral position of the plunger is adjusted nearer to the valve-opened end to reduce the electric power consumption.
However, a required length of the stroke of the valve element of the engine, or the required period for the valve-opening condition of the intake valve or the exhaust valve of the engine, is not uniform in the whole range of the engine operation. In order to provide the engine with a desired level of the intake air, it is desirable to make the stroke of the valve element when the quantity of intake air into the engine is small shorter than the stroke of the valve element when the quantity of intake air is great.
A valve operating apparatus in which the valve element (the intake valve or the exhaust valve) is operated by an electromagnetic force is taken into account. If the stroke of the valve element is longer, the electromagnetic force required to operate the valve element must be increased. To increase the required electromagnetic force, the required electric power consumption must be increased.
Accordingly, in order to ensure a reduction of the electric power consumption in the whole range of the engine operation, it is desirable to provide a valve operating apparatus that is capable of suitably modifying the length of the stroke of the valve element and capable of suitably modifying the neutral position of the valve element.
Although the above conventional device can modify the neutral position of the valve element, it is impossible to modify the length of the stroke of the valve element. Therefore, it is difficult that the above conventional device effectively reduces the electric power consumption in the whole range of the engine operation in order to provide a desired level of output characteristics of the engine.